For the most part I am a borrower. I prefer the library because I only want to read most books once. I do a lot of reading, but not all of it is worth a second read. So what is the point in buying a book if I don't know that I will like it?
I do buy books that are my favorites. If I have already read it and I know I want to read it again, then it is worth owning. I also am getting into the habit of buying classics whenever I see them at thrift stores. The basis of our homeschooling method is reading classics, so I'm trying to build up our inventory. It's also important to me that we have a lot of books in our home to inspire our children and show them what is most important.